* Alexey Perevalov (a.pereva...@samsung.com) wrote:
> This modification is necessary for userfault fd features which are
> required to be requested from userspace.
> UFFD_FEATURE_THREAD_ID is a one of such "on demand" feature, which will
> be introduced in the next patch.
>
> QEMU have to use separate userfault file descriptor, due to
> userfault context has internal state, and after first call of
> ioctl UFFD_API it changes its state to UFFD_STATE_RUNNING (in case of
> success), but kernel while handling ioctl UFFD_API expects
> UFFD_STATE_WAIT_API.
> So only one ioctl with UFFD_API is possible per ufd.
>
> Signed-off-by: Alexey Perevalov <a.pereva...@samsung.com>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
> ---
> migration/postcopy-ram.c | 94
> ++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 88 insertions(+), 6 deletions(-)
>
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index 8838901..cbe8f9f 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -63,16 +63,67 @@ struct PostcopyDiscardState {
> #include <sys/eventfd.h>
> #include <linux/userfaultfd.h>
>
> -static bool ufd_version_check(int ufd, MigrationIncomingState *mis)
> +
> +/**
> + * receive_ufd_features: check userfault fd features, to request only
> supported
> + * features in the future.
> + *
> + * Returns: true on success
> + *
> + * __NR_userfaultfd - should be checked before
> + * @features: out parameter will contain uffdio_api.features provided by
> kernel
> + * in case of success
> + */
> +static bool receive_ufd_features(uint64_t *features)
> {
> - struct uffdio_api api_struct;
> - uint64_t ioctl_mask;
> + struct uffdio_api api_struct = {0};
> + int ufd;
> + bool ret = true;
> +
> + /* if we are here __NR_userfaultfd should exists */
> + ufd = syscall(__NR_userfaultfd, O_CLOEXEC);
> + if (ufd == -1) {
> + error_report("%s: syscall __NR_userfaultfd failed: %s", __func__,
> + strerror(errno));
> + return false;
> + }
>
> + /* ask features */
> api_struct.api = UFFD_API;
> api_struct.features = 0;
> if (ioctl(ufd, UFFDIO_API, &api_struct)) {
> error_report("%s: UFFDIO_API failed: %s", __func__,
> strerror(errno));
> + ret = false;
> + goto release_ufd;
> + }
> +
> + *features = api_struct.features;
> +
> +release_ufd:
> + close(ufd);
> + return ret;
> +}
> +
> +/**
> + * request_ufd_features: this function should be called only once on a newly
> + * opened ufd, subsequent calls will lead to error.
> + *
> + * Returns: true on succes
> + *
> + * @ufd: fd obtained from userfaultfd syscall
> + * @features: bit mask see UFFD_API_FEATURES
> + */
> +static bool request_ufd_features(int ufd, uint64_t features)
> +{
> + struct uffdio_api api_struct = {0};
> + uint64_t ioctl_mask;
> +
> + api_struct.api = UFFD_API;
> + api_struct.features = features;
> + if (ioctl(ufd, UFFDIO_API, &api_struct)) {
> + error_report("%s failed: UFFDIO_API failed: %s", __func__,
> + strerror(errno));
> return false;
> }
>
> @@ -84,11 +135,42 @@ static bool ufd_version_check(int ufd,
> MigrationIncomingState *mis)
> return false;
> }
>
> + return true;
> +}
> +
> +static bool ufd_check_and_apply(int ufd, MigrationIncomingState *mis)
> +{
> + uint64_t asked_features = 0;
> + static uint64_t supported_features;
> +
> + /*
> + * it's not possible to
> + * request UFFD_API twice per one fd
> + * userfault fd features is persistent
> + */
> + if (!supported_features) {
> + if (!receive_ufd_features(&supported_features)) {
> + error_report("%s failed", __func__);
> + return false;
> + }
> + }
> +
> + /*
> + * request features, even if asked_features is 0, due to
> + * kernel expects UFFD_API before UFFDIO_REGISTER, per
> + * userfault file descriptor
> + */
> + if (!request_ufd_features(ufd, asked_features)) {
> + error_report("%s failed: features %" PRIu64, __func__,
> + asked_features);
> + return false;
> + }
> +
> if (getpagesize() != ram_pagesize_summary()) {
> bool have_hp = false;
> /* We've got a huge page */
> #ifdef UFFD_FEATURE_MISSING_HUGETLBFS
> - have_hp = api_struct.features & UFFD_FEATURE_MISSING_HUGETLBFS;
> + have_hp = supported_features & UFFD_FEATURE_MISSING_HUGETLBFS;
> #endif
> if (!have_hp) {
> error_report("Userfault on this host does not support huge
> pages");
> @@ -149,7 +231,7 @@ bool
> postcopy_ram_supported_by_host(MigrationIncomingState *mis)
> }
>
> /* Version and features check */
> - if (!ufd_version_check(ufd, mis)) {
> + if (!ufd_check_and_apply(ufd, mis)) {
> goto out;
> }
>
> @@ -525,7 +607,7 @@ int postcopy_ram_enable_notify(MigrationIncomingState
> *mis)
> * Although the host check already tested the API, we need to
> * do the check again as an ABI handshake on the new fd.
> */
> - if (!ufd_version_check(mis->userfault_fd, mis)) {
> + if (!ufd_check_and_apply(mis->userfault_fd, mis)) {
> return -1;
> }
>
> --
> 1.9.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
